Gram Staining of Coxiella burnetii

Abstract

The observation that Coxiella burnetii [Rickettsia burneti] sometimes behaved as a Gram-variable organism when stained by the Gram-Nicolle technique, led the author to examine its reactions to other modifications of the Gram staining procedure. Clear-cut results were obtained by primary staining with a mixture of equal volumes of 1% aqueous crystal violet and 5% aqueous sodium bicarbonate (mixture prepared fresh; not suitable after 1 hour), steamed for 1 minute; mordanting for 1 minute with an aqueous solution containing 1% iodine and 2% potassium iodide; and decolorizing for 18 seconds with ethyl alcohol-acetone (4 volumes of 95% ethyl alcohol plus 1 volume of acetone). R. burneti was strongly Gram-positive; R. prowazeki, R. mooseri, R. ricketfsii, R. akari, R. tsutsugamushi and psittacosis organisms were Gram-negative. It is suggested that this procedure may enable R. burneti to be rapidly distinguished from other rickettsiae in new isolates. R. S. F. Hennessey.